Great Q&A - Weight Fluctuation

Very well written summary of why you see frequent (and sometimes dramatic) short-term fluctuations in weight.

From: http://www.cnn.com/2010/HEALTH/expert.q.a/10/08/water.weight.fluctuates.jampolis/index.html

How is it possible for my weight to fluctuate so much?
Panzene, Ocala, Florida

I've noticed that I gained what I'm assuming to be water weight. I gained four pounds in a 24-hour period. I recently started a lot of exercise and weight training and was told that I'm not drinking enough water. I took two days of drinking at least three liters of water and just doing cardio and noticed that I went from 169 to 163, but the third day I checked my weight again and was back to 168. How is this possible?


Diet and Fitness Expert
Dr. Melina Jampolis
Physician Nutrition Specialist

Expert answer
Hi Panzene -- First of all let me congratulate you on beginning what sounds like a great exercise and strength training program. You are absolutely correct in your assumption that your weight fluctuations are mostly due to water weight.

Basic laws of physics would not allow you to gain four pounds of fat in such a short period unless you ate an extra 14,000 calories (each pound of fat contains 3,500 calories). Mild dehydration may cause fluid retention, which can increase scale weight, which may be one of the reasons your weight dropped with increased water intake.

Another reason may be due to the fact that training muscles, especially if you are new to weight lifting, causes micro tears in the muscle, which is how muscle is built. This can lead to fluid retention in the muscle itself for a couple of days.

I'm not sure if you trained with weights or dropped your water intake on the third day, but this could have led to the increase or may just represent your stabilized weight (which would indicate a one-pound loss in three days, which is great).

Your weight can also be affected by carbohydrate consumption, so if you decreased your carbohydrate intake during the initial two days and then had a high-carbohydrate dinner the evening before the third day, this could have led to water loss and then gain because stored carbohydrates, like muscle, also hold water. This is why low-carb diets seem to work so dramatically in the early stages -- stored carbohydrates and water are lost in addition to fat and muscle.

Daily water fluctuations, which are more common in women because of hormonal changes throughout the month, are one of the main reasons that I tell my patients not to weigh themselves every day, especially if they are just starting an exercise program. I prefer that they track their measurements regularly, which are a much better indicator of fat loss and muscle gain.

If you are starting an exercise program and find that you are steadily continuing to gain weight over time, evaluate your diet closely for hidden or extra calories. Some people find that exercise increases their appetite, so they may be consuming even more calories than they are burning thereby gaining muscle and fat at the same time. I find sports drinks and energy bars to be common sources of extra calories that may be getting in the way of fat loss.

It is important to remember that most people cannot gain more than one to two pounds of muscle per month, so the increase in the scale in 24 hours could not represent actual muscle gain.

Other potential causes of short-term weight gain are increased sodium intake (eating a salty dinner the night before can cause a jump in scale weight), constipation and even long-distance travel, which may cause fluid retention and dehydration. So my advice is to stop weighing yourself daily, watch your calorie consumption, and focus on inches rather than pounds for now.